Imagine “Star Wars” if a city-sized tank with a Union Jack was the Death Star and everybody was trying to be Han Solo, and you get the gist of the post-post-apocalyptic epic “Mortal Engines.”

Philip Reeve’s young-adult book gets an expansive world-building adaptation courtesy of a master. Peter Jackson (“The Lord of the Rings”) co-writes and produces while his protégé Christian Rivers makes his directorial debut (★★½ out of four; rated PG-13; in theaters nationwide Dec. 14) with a tale of freedom fighters rallying to take on the antagonistic London, a supervillain on treads that eats smaller cities in a motorized landscape before it literally rolls over the entire globe.

Indeed, this is the kind of visual spectacle where Jackson excels, like “Mad Max” meets “Godzilla,” with cool airborne metropolises, all manner of winged and wheeled vehicles, a Terminator-like undead robotic guy and dizzying action. Unfortunately, there’s not much room left for fleshed-out personalities or narrative depth, making the whiz-bang wonder often feel too empty.

“Mortal Engines” is set several centuries after the calamitous Sixty Minute War, wherein civilization was wiped out – save for some choice souvenirs that nerdy historian Tom Natsworthy (Robert Sheehan) keeps safe in a museum onboard London. (The guy is a true connoisseur of vintage toasters.)

The great predator city of London (left) hunts down moving small towns to take their resources, human and otherwise, in "Mortal Engines."(Photo: UNIVERSAL PICTURES/MRC)

Mankind now lives life in various forms of transportation on the ground or in the air, and the British municipality is a predator city – with St. Paul’s Cathedral sitting atop it – rumbling across the land and gobbling up resources. But even those are running low after running down so many mobile locales.

Thaddeus Valentine (Hugo Weaving) is a London power player with nefarious machinations to break through a gigantic wall in Asia, which would lead to a whole new hunting ground. But Valentine has enemies, chiefly the mysterious masked assassin Hester Shaw (Hera Hilmar).

Blaming him for her mother’s death, Hester sneaks aboard London and takes a shot at Valentine but Tom gets in the way. This chance meeting ends with Hester and Tom getting hurled outside and into an adventure, where the two meet uber-cool outlaw Anna Fang (Jihae); are hunted by Shrike (Stephen Lang), the half-man, half-machine dude who raised Hester; and fall in with the Anti-Traction League just in time for the blitzkrieg of a finale, with dogfights and derring-do.

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Oh, yeah, Tom and Hester also fall for each other in this “Star Wars”-on-wheels action-fest that clearly wears its inspirations on its mechanical sleeve. Hester is an awesome young warrior with facial scars, a no-nonsense disposition and a tragic backstory, though you’re puzzled at times with what she sees in Tom, a total Luke Skywalker who whines a lot before finding his heroic mojo.

There are many more Hans running around, namely Anna Fang and her fellow pilots flying in neato warships. Quite a few characters, though – not just extras, but named characters high up in the credits – simply fulfill their plot point and then disappear. There are some seriously high stakes involved, yet it's all for naught when you're rooting for Hester and ambivalent about everyone else.

“Mortal Engines” is the kind of mythology you want a franchise guru such as Jackson making his own, with popcorn-chomping thrills and endless ambition doing more good than harm. It’s also a huge fascinating universe meant for a sprawling HBO series, not a mashed-up two hours and change. As a result, the storytelling execution is just not totally there, a flat tire on the highway to being the next big thing.